The present invention relates to a device which forms the selvedge of a woven fabric and is disposed in a loom.
U.S. Pat. No. 3,320,978 discloses a device for forming a selvedge which comprises a rotatable member and two guides for guiding yarns for the selvedge mounted on the rotatable member. As the rotatable member rotates, the selvedge yarn guides rotate on their axes and revolve. As a result, the two selvedge yarns are open and closed and they are twisted at every weaving.
The above-mentioned conventionally known device for forming a selvedge wherein the selvedge yarns are open and closed by the rotational movement of the rotatable member and are twisted at every weaving is disposed immovably in any direction, i.e., along the lengthwise direction, the vertical direction and the widthwise direction of the machine frame, and the device is disposed at a position which corresponds to the maximum number of the heald frames. In other words, even if the number of the heald frames is changed, the position of the device for forming the selvedge cannot be changed. Accordingly, the forwardmost position of the droppers which are disposed behind the device for forming the selvedge is limited, and the backward closed position of the warps is determined on the basis of the limited forward position of the droppers regardless of the number of the heald frames. As a result, if the number of the heald frames is decreased, an unnecessary space is formed between the heald frames and the device for forming the selvedge. In addition, the distance between the backwardmost heald frame and the cloth fell becomes unequal to the distance between the backwardmost heald frame and the backward closed position of the warps. As a result, the tension in the warps cannot be adjusted appropriately, and a woven fabric which has an inferior weave and hand is produced.
Since in such a conventional device for forming a selvedge the positions where the selvedge yarn bobbins are supported are also limited, the opening angle between the selvedge yarns is constant if the device for forming a selvedge is disposed at a certain position. Accordingly, the opening angle between the selvedge yarns is not necessarily equal to the opening angle formed between the ground warps. In a loom, such as a jet loom, wherein the front end of the weft is free, the selvedge yarn may interfere with the weft, and as a result, weft stop may occur. It should be noted that the weft is woven at will in accordance with the weaving condition along the lower warps or along the upper warps while the warps are open. For example, when the device for forming a selvedge is disposed so that the selvedge yarn is open in alignment with the lower warps of the ground warps, the upper selvedge yarn interferes with the weft and weft stop frequently occurs if the weaving position is changed in order to weave the weft along the upper warps. In addition, in a loom wherein the device for forming a selvedge is disposed behind the heald frames for supporting ground heddles, it is necessary that the position of the device for forming a selvedge be changed when the number of the heald frames for supporting ground heddles is changed. In such a case, the opening angle between the selvedge yarns may be changed as the position of the device is changed. If the number of the heald frames for supporting ground heddles is increased, the device for forming a selvedge is displaced away from the heald frames, and then the opening angle between the selvedge yarns becomes small. As a result, there occurs the interference of the selvedge yarn with the woven weft because of the reason mentioned above, and in addition, the interference of the selvedge yarn with the woven weft, for example, the lower selvedge yarn per se is positioned higher than the lower warps of the ground warps. To improve the weave and hand of the obtained woven fabric, in some looms, the warps are closed at a position higher than the warp line, and in some looms, the warps are closed at a position lower than the warp line. However, it should be noted that since in the above-mentioned conventional device for forming a selvedge the selvedge yarns are open by means of the rotational movement of the rotational member, the selvedge yarns are closed at a position near the warp line. In other words, the height of the closed position of the selvedge yarns is different from the height of the closed position of the ground warps, and as a result, the formation of the selvedge is adversely affected. For example, when the warps are closed at a position lower than the warp line, if the conventional device for forming a selvedge is disposed in order to close the selvedge yarns at a position lower than the warp line, it is impossible to overcome the change of the warping condition wherein the ground warps are closed at a position higher than the warp lines.